1. Field of the Invention
The present invention pertains to a security technique such as for data in an interface between devices and to, for example, a technique for preventing leakage or the like of the data exchanged between ICs.
2. Description of the Related Art
Environment of the development and diffusion of multimedia has been prepared through progress in the digitization technique. Since information formed into digital data does not change its quality even in processing such as storing, reproducing, communicating, its application has been steadily expanded.
Through an information content compression technique or the like, information such as not only characters and graphics but also voice and video has been able to be processed, stored, and reproduced digitally.
In the back of these techniques, infringement of copyright and the like through an illegal copy or the like has become a problem, and thus various technical methodology for preventing reproduction of written materials or the like have been taken. For example, SCMS (Serial Copy Management System) is implemented in the CD, MD, DAT, CD-R, and the like for music, and CGMS (Copy Generation Management System) or the like is implemented in the DVD (Digital Versatile Disk).
A typical example of a digital music player in which a memory card is employed is shown in FIG. 1.
Audio data such as in music which is formed into digital data are compressed, for example, by an information content compression technique, and after specific cryptography is incorporated in a specific portion by a copy protection technique, those audio data are recorded in a memory card 111.
The data recorded in the memory card 111 are read by the a card I/F section 121, cryptography incorporated in the data is decrypted by a decryption section 122, data compressed are decoded by a compressed signal decode section 131 and are converted into an analog signal by a DAC (Digital-Analog Converter) section 141 so as to be sent to an output device such as a speaker. In the drawing, the parts shown by broken lines show configurational units of the apparatus, and the present digital music player is composed of a card slot 110 holding the memory card 111, an IC-120 having the card I/F section 121 and the decryption section 122, an IC-130 having the compressed signal decode section 131, and an IC-140 having the DAC section 141. The respective devices or blocks are connected by wiring 151 to 154.
As shown in the drawing, since the data flowing between the card slot 110 and the IC-120 are encrypted in advance, the confidentiality thereof is maintained. However, on and after the IC-120, that is, the data flowing between the IC-120 and the IC-130 and between the IC-130 and the IC-140 are digital data whose cryptography is released by the decryption section 122 in order to reproduce music data. Specifically, the data flowing between the IC-130 and the IC-140 are the data further decoded by the compressed signal decode section 131. Accordingly, it is not impossible to connect a measuring device such as a probe to the wiring portions 153, 154 to absorb data so as to use them wrongly.
That is, it is the present situation that although a copy protection technique employed conventionally is applied to an interface section provided in the external of an apparatus such as in between a memory card and a music player, it has not fully covered, for example, an interface between ICs inside a music player apparatus.
In order to solve such problem in a digital music player as shown in FIG. 1, although a method may be thought wherein the IC-120, the IC-130, the IC-140 are formed into one chip, such method is difficult to be realized actually due to problems in a manufacturing cost, a technical problem, and the like.
In general, in such interface between ICs, terminals are specified by data, clock, a latch signal, or the like, and by employing a measuring device, a signal flowing between ICs can be surmised, and even the data transferred may be read. In some cases, data may be exchanged between ICs in a state without any cryptography or scrambling depending on the data.
Further, since, for example, music data, video data, or the like have only several types of transfer formats, specifying a format is easy, and thus such data are likely to be falsely copied in a state where a copyrighted material is a high grade digital signal. With respect to data having a high concealment property, a protection such as cryptography is given to the data themselves in advance, but an interface between chips inside an apparatus is often in a defenseless state.
This type of problem exists not only regarding a reproduction device for music or video software but also similarly regarding an information processing apparatus, for example, for operating a computer program or game software and also is contained in an information transmission means or the like employing a network or a digital broadcast.